/*
 *  This file is a part of TiledArray.
 *  Copyright (C) 2013  Virginia Tech
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *  Justus Calvin
 *  Department of Chemistry, Virginia Tech
 *
 *  add.h
 *  April 24, 2012
 *
 */

#ifndef TILEDARRAY_PMAP_BLOCKED_PMAP_H__INCLUDED
#define TILEDARRAY_PMAP_BLOCKED_PMAP_H__INCLUDED

#include <TiledArray/error.h>
#include <TiledArray/pmap/pmap.h>
#include <TiledArray/madness.h>
#include <algorithm>

namespace TiledArray {
  namespace detail {

    /// A blocked process map

    /// Map N elements among P processes into blocks that are approximately N/P
    /// elements in size. A minimum block size may also be specified.
    class BlockedPmap : public Pmap {
    protected:

      // Import Pmap protected variables
      using Pmap::rank_; ///< The rank of this process
      using Pmap::procs_; ///< The number of processes
      using Pmap::size_; ///< The number of tiles mapped among all processes
      using Pmap::local_; ///< A list of local tiles

    private:

      const size_type block_size_; ///< block size (= size_ / procs_)
      const size_type remainder_; ///< tile remainder (= size_ % procs_)
      const size_type block_size_plus_1_; ///< Cashed value
      const size_type block_size_plus_1_times_remainder_; ///< Cached value
      const size_type local_first_; ///< First tile of this process's block
      const size_type local_last_; ///< Last tile + 1 of this process's block

    public:
      typedef Pmap::size_type size_type; ///< Key type

      /// Construct Blocked map

      /// \param world The world where the tiles will be mapped
      /// \param size The number of tiles to be mapped
      BlockedPmap(madness::World& world, size_type size) :
          Pmap(world, size),
          block_size_(size_ / procs_),
          remainder_(size_ % procs_),
          block_size_plus_1_(block_size_ + 1),
          block_size_plus_1_times_remainder_(remainder_ * block_size_plus_1_),
          local_first_(rank_ * block_size_ + std::min<size_type>(rank_, remainder_)),
          local_last_((rank_ + 1) * block_size_ + std::min<size_type>((rank_ + 1), remainder_))
      {
        local_.reserve(local_last_ - local_first_);


        // Construct a map of all local processes
        for(size_type first = local_first_; first < local_last_; ++first) {
          TA_ASSERT(BlockedPmap::owner(first) == rank_);
          local_.push_back(first);
        }
      }

      virtual ~BlockedPmap() { }

      /// Maps \c tile to the processor that owns it

      /// \param tile The tile to be queried
      /// \return Processor that logically owns \c tile
      virtual size_type owner(const size_type tile) const {
        TA_ASSERT(tile < size_);
        return (tile < block_size_plus_1_times_remainder_ ?
            tile / block_size_plus_1_ :
            ((tile - block_size_plus_1_times_remainder_) / block_size_) + remainder_);
      }


      /// Check that the tile is owned by this process

      /// \param tile The tile to be checked
      /// \return \c true if \c tile is owned by this process, otherwise \c false .
      virtual bool is_local(const size_type tile) const {
        return ((tile >= local_first_) && (tile < local_last_));
      }
    }; // class BlockedPmap

  }  // namespace detail
}  // namespace TiledArray


#endif // TILEDARRAY_PMAP_BLOCKED_PMAP_H__INCLUDED
